# What is Density function: Definition and 192 Discussions

In probability theory, a probability density function (PDF), or density of a continuous random variable, is a function whose value at any given sample (or point) in the sample space (the set of possible values taken by the random variable) can be interpreted as providing a relative likelihood that the value of the random variable would equal that sample. In other words, while the absolute likelihood for a continuous random variable to take on any particular value is 0 (since there is an infinite set of possible values to begin with), the value of the PDF at two different samples can be used to infer, in any particular draw of the random variable, how much more likely it is that the random variable would equal one sample compared to the other sample.
In a more precise sense, the PDF is used to specify the probability of the random variable falling within a particular range of values, as opposed to taking on any one value. This probability is given by the integral of this variable's PDF over that range—that is, it is given by the area under the density function but above the horizontal axis and between the lowest and greatest values of the range. The probability density function is nonnegative everywhere, and its integral over the entire space is equal to 1.
The terms "probability distribution function" and "probability function" have also sometimes been used to denote the probability density function. However, this use is not standard among probabilists and statisticians. In other sources, "probability distribution function" may be used when the probability distribution is defined as a function over general sets of values or it may refer to the cumulative distribution function, or it may be a probability mass function (PMF) rather than the density. "Density function" itself is also used for the probability mass function, leading to further confusion. In general though, the PMF is used in the context of discrete random variables (random variables that take values on a countable set), while the PDF is used in the context of continuous random variables.

View More On Wikipedia.org
1. ### I Density fluctuations and the color of the sky

From posts like this I get that the color of the sky is explained by Rayleigh scattering, but needs density fluctuations. However as atoms are not uniform and are localized, the density is $$\rho(\mathbf r)=\sum_i \delta(\mathbf r-\mathbf r_i)$$ where ##i## sums over all the atom positions...
2. ### Solve this problem that involves a probability density function

I am refreshing on this; ..after a long time... Note that i do not have the solution to this problem. I will start with part (a). ##f(u)= 3u-\dfrac{3u^2}{2k}## with limits ##0≤u≤k## it follows that, ##3k - \dfrac{3k}{2}=1## ##\dfrac{3k}{2}=1## ##k=\dfrac {2}{3}## For part (b)...
3. ### Solve the problem involving probability density function

This is the question: This is the ms solution- from Further Maths paper. My question is referenced to the highlighted part. I can see they substituted for the lower limit i.e ##x=1## to get: ##F(x)=\dfrac{x^3-1}{63}## supposing our limits were; ##2≤x≤4## would the same approach apply? Anything...
4. ### Using Gauss's Law to Calculate Charge Density Function

I've attached what I have so far. Used Gauss's law, everything seemed to make sense except the units don't work out in the end. The charge density function if given by: r(z)=az, where z is the perpendicular distance inside the plane.
5. ### Problem involving Probability density function

I just want to be certain, i think the inequality indicated is not correct...ought to be less than. Kindly confirm...This is a textbook literature.
6. ### A Solving an Integral involving a probability density function

In an article written by Richard Rollleigh, published in 2010 entitled The Double Slit Experiment and Quantum Mechanics, he argues as follows: "For something to be predictable, it must be a consistent measurement result. The positions at which individual particles land on the screen are not...
7. ### I The probability density function for the double-slit experiment

I am desperate. I've scoured the web for the formula for the probability density function for the interference pattern obtained in the double slit experiment with both slits open. So I want to know the probability density function and not the intensity function. I prefer not to have references...

9. ### Random variable and probability density function

Hi, I was trying to solve the attached problem which shows its solution as well. I cannot understand how and where they are getting the equations 3.69 and 3.69A from. Are they substituting the values of θ₁ and θ₂ into Expression 1 after performing the differentiation to get equations 3.70 and...
10. ### A Probability Density Function: Converting Experimental Observations to PDF

Hi All I am currently doing Master in data science. I came across the function PDF probability density function which is used to find cumulative probability(range) of a continuous random variable. The PDF probability density function is plotted against probability density in y-axis and...
11. ### A The name of this probability density function

Does anyone knows the name of the probability density function f(y) =aeby-cy2
12. ### I Find P(X+Y>1/2) for given joint density function

Hey everybody, :smile: I have a joint density of the random variables ##X## and ##Y## given and want to find out ##P(X+Y>1/2)##. The joint density is as follows: $$f_{XY}(x,y) = \begin{cases}\frac{1}{y}, &0<x<y,0<y<1 \\ 0, &else \end{cases}$$ To get a view of this I created a plot: As...
13. ### Finding marginal distribution of 2d of probability density function

Hi, I have question about finding marginal distributions from 2d marginal pdfs that lead to the probabilities being greater than 1. Question: If we have the joint probability distribution ## f(x, y) = k \text{ for} |x| \leq 0.5 , |y| \leq 0.5 ## and 0 otherwise. I have tried to define a square...

43. ### Determine charge at origin, based on charge density function

Homework Statement a) and b) are no problem. I need help to solve c) and d) Homework Equations c) Delta dirac function Gauss' law d) Gauss' law ## \int_V {\rho \, d\tau} = Q_{enclosed} ## The Attempt at a Solution By taking laplace on the potential I get: ## \rho(\mathbf{r}) =...
44. ### Probability density function of simple Mass-Spring system.

Homework Statement We know that after long run of simple mass-spring system, there should be a probability of finding the mass at certain points between -A and A.. Obviously in probability of finding the particle near A or -A is higher than finding the particle at 0, because the speed is the...
45. ### Probability density function of uniform distribution

Homework Statement Random variable X is uniformly distributed on interval [0,1]: f(x)=\begin{cases} 1 & \text{ if } 0\leq x\leq 1\\ 0 & \text{ else} \end{cases} a) Find probability density function ρ(y) of random variable Y=\sqrt{X} +1 I tried like this. Is it good, if no why not...
46. ### Joint problem density function problem

I need help guys I can't understand this Can anyone explain thoroughly how do I form the range for this question? f(x,y)= e-x for 0≤x≤y≤∞ 0 Otherwise Find P(x+y≤1) I attempted this by integrating through the range of 0≤y≤(1-x) and 0≤x≤∞ but that...
47. ### What are the Properties of Joint Density Functions?

Hello, Homework Statement The joint probability density function of X and Y is given by f(x,y)=c*1(|y|<x<1) 1 is the indicator function -Find c -Find the marginal densities of X and Y -Find the means, variances and the covariance -Find conditional densities, means and variances of X given...
48. ### Density function for a normal distribution

Homework Statement I have to prove that ## \int e^{\frac{x^2}{-2}}dx ## from +∞ to -∞ = ##\sqrt{2\pi} ## Homework Equations N/A The Attempt at a Solution My GSI went from 1) ## \int e^{\frac{x^2}{-2}}dx ## from +∞ to -∞ = ##\sqrt{2\pi} ## to 2) ## (\int e^{\frac{x^2}{-2}}dx)(\int...
49. ### Probability Question - Joint density function

Before I begin, here is the question: If the PDF of two independent random variables X and Y are: f(x) = exp(-x)u(x) f(y) = exp(-y)u(y) Determine the join probability density function (JPDF) of Z&W defined by: Z = X+Y W = X/(X+Y). So, I know how to solve this except for one thing. How do I get...
50. ### What is a Probabilty Density Function?

What really is a probability density function for continuous random variables? I know that the probability for a single value occurring in a continuous probability distribution is so infinitesimal that it is considered 0, which is why we use the cumulative distribution function that is the the...